The present invention relates to a radiator fan arrangement for a vehicle and particularly to an arrangement including the continuously operated cooling fan and another selectively operable cooling fan.
A vehicle powered by a combustion engine usually comprises a radiator for cooling the coolant which cools the combustion engine. A radiator fan is usually arranged close to the radiator in order to provide a forced air flow through the radiator with the object of cooling the coolant. Conventional radiator fans are usually powered by the combustion engine via a permanent mechanical connection. The magnitude of the air flow which the radiator fan generates through the radiator will thus vary with the engine's speed. Many heavy vehicles are powered by supercharged combustion engines. A charge air cooler is used for cooling the supercharged air before it is led to the combustion engine. A charge air cooler is usually situated in front of the ordinary radiator at the front portion of the vehicle. In some cases a condenser of an air conditioning system may also be situated close to the vehicle's front portion, as also an EGR cooler for cooling of returned exhaust gases.
Where one or more such cooling elements are arranged in front of an ordinary radiator, the air flow reaching the radiator will be at a higher temperature. The coolant cooled in the radiator will thus be subject to a reduced cooling effect. To compensate for this reduced cooling effect, a greater air flow may be forced through the coolers. One way of increasing the air flow through the coolers is to provide the ordinary radiator fan's mechanical connection to the combustion engine with a higher gear ratio, but for practical reasons it is only possible to increase the gear ratio up to a certain limit. When there is a high ambient temperature and the combustion engine is running at low speed, it may therefore be difficult to provide enough air flow through the coolers to effect acceptable cooling of, above all, the coolant, since these coolers are often situated downstream from one or more other cooling elements with respect to the direction of the cooling air flow.
U.S. Pat. No. 3,894,521 refers to a radiator fan which provides an air flow through a radiator for cooling of coolant and a condenser of an air conditioning system. In that case, the radiator fan is connected to an engine and an electric motor via separate coupling mechanisms so that either the engine or the electric motor can be used for powering the radiator fan. When the engine rotates at a speed which is too low for the radiator fan to supply a necessary air flow through the radiator, the electric motor takes over the operation of the radiator fan momentarily and imparts to it a higher speed.